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Subject[RFC 4/4] {RFC} kmod.c: Add new call_usermodehelper_timeout() API

In the blasphemous occasions that a the Kernel must call a user-mode program
half of the times it is more robust to not wait forever but limit the wait
for a specified timeout.

So add a new call_usermodehelper_timeout() that implements that.
(Users of this new API will be added once this API is in mainline)

call_usermodehelper_fns() is added an extra timeout parameter which
is then implemented in call_usermodehelper_exec. The few users of
call_usermodehelper_fns() are also changed in this patch.

Since now the executing threads might come back after the waiting
thread has returned, do to a timeout. I used a simple kref pattern
to govern the life time of the subprocess_info struct.

Should some wait-forever callers today, be converted to this new
schema?

CC: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
---
fs/exec.c | 2 +-
include/linux/kmod.h | 15 +++++++++++++--
kernel/kmod.c | 29 +++++++++++++++++++++--------
kernel/sys.c | 2 +-
security/keys/request_key.c | 2 +-
5 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 92ce83a..e696081 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -2197,7 +2197,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
}

retval = call_usermodehelper_fns(helper_argv[0], helper_argv,
- NULL, UMH_WAIT_EXEC, umh_pipe_setup,
+ NULL, UMH_WAIT_EXEC, 0, umh_pipe_setup,
NULL, &cprm);
argv_free(helper_argv);
if (retval) {
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 5a89c00..eccc3f5 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -25,6 +25,7 @@
#include <linux/compiler.h>
#include <linux/workqueue.h>
#include <linux/sysctl.h>
+#include <linux/kref.h>

#define KMOD_PATH_LEN 256

@@ -55,12 +56,14 @@ enum umh_wait {
};

struct subprocess_info {
+ struct kref kref;
struct work_struct work;
struct completion *complete;
char *path;
char **argv;
char **envp;
enum umh_wait wait;
+ unsigned long wait_timeout;
int retval;
int (*init)(struct subprocess_info *info, struct cred *new);
void (*cleanup)(struct subprocess_info *info);
@@ -69,14 +72,22 @@ struct subprocess_info {

extern int
call_usermodehelper_fns(char *path, char **argv, char **envp,
- enum umh_wait wait,
+ enum umh_wait wait, unsigned long timeout,
int (*init)(struct subprocess_info *info, struct cred *new),
void (*cleanup)(struct subprocess_info *), void *data);

static inline int
call_usermodehelper(char *path, char **argv, char **envp, enum umh_wait wait)
{
- return call_usermodehelper_fns(path, argv, envp, wait,
+ return call_usermodehelper_fns(path, argv, envp, wait, 0,
+ NULL, NULL, NULL);
+}
+
+static inline int
+call_usermodehelper_timeout(char *path, char **argv, char **envp,
+ enum umh_wait wait, unsigned long timeout)
+{
+ return call_usermodehelper_fns(path, argv, envp, wait, timeout,
NULL, NULL, NULL);
}

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 3cb7457..a72eefa 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -129,7 +129,7 @@ int __request_module(bool wait, const char *fmt, ...)
trace_module_request(module_name, wait, _RET_IP_);

ret = call_usermodehelper_fns(modprobe_path, argv, envp,
- wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC,
+ wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC, 0,
NULL, NULL, NULL);

atomic_dec(&kmod_concurrent);
@@ -191,8 +191,11 @@ fail:
do_exit(0);
}

-static void call_usermodehelper_freeinfo(struct subprocess_info *info)
+static void call_usermodehelper_freeinfo(struct kref *kref)
{
+ struct subprocess_info *info =
+ container_of(kref, struct subprocess_info, kref);
+
if (info->cleanup)
(*info->cleanup)(info);
kfree(info);
@@ -235,6 +238,7 @@ static int wait_for_helper(void *data)
}

complete(sub_info->complete);
+ kref_put(&sub_info->kref, call_usermodehelper_freeinfo);
return 0;
}

@@ -258,7 +262,8 @@ static void __call_usermodehelper(struct work_struct *work)

switch (wait) {
case UMH_NO_WAIT:
- call_usermodehelper_freeinfo(sub_info);
+ kref_put(&sub_info->kref, call_usermodehelper_freeinfo);
+ kref_put(&sub_info->kref, call_usermodehelper_freeinfo);
break;

case UMH_WAIT_PROC:
@@ -269,6 +274,7 @@ static void __call_usermodehelper(struct work_struct *work)
if (pid < 0)
sub_info->retval = pid;
complete(sub_info->complete);
+ kref_put(&sub_info->kref, call_usermodehelper_freeinfo);
}
}

@@ -387,6 +393,7 @@ struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
if (!sub_info)
goto out;

+ kref_init(&sub_info->kref);
INIT_WORK(&sub_info->work, __call_usermodehelper);
sub_info->path = path;
sub_info->argv = argv;
@@ -452,22 +459,27 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,

sub_info->complete = &done;
sub_info->wait = wait;
+ if (!sub_info->wait_timeout)
+ sub_info->wait_timeout = MAX_SCHEDULE_TIMEOUT;

+ /* Balanced in __call_usermodehelper or wait_for_helper */
+ kref_get(&sub_info->kref);
queue_work(khelper_wq, &sub_info->work);
if (wait == UMH_NO_WAIT) /* task has freed sub_info */
goto unlock;
- wait_for_completion(&done);
- retval = sub_info->retval;
-
+ if (likely(wait_for_completion_timeout(&done, sub_info->wait_timeout)))
+ retval = sub_info->retval;
+ else
+ retval = -ETIMEDOUT;
out:
- call_usermodehelper_freeinfo(sub_info);
+ kref_put(&sub_info->kref, call_usermodehelper_freeinfo);
unlock:
helper_unlock();
return retval;
}

int call_usermodehelper_fns(char *path, char **argv, char **envp,
- enum umh_wait wait,
+ enum umh_wait wait, unsigned long timeout,
int (*init)(struct subprocess_info *info, struct cred *new),
void (*cleanup)(struct subprocess_info *), void *data)
{
@@ -480,6 +492,7 @@ int call_usermodehelper_fns(char *path, char **argv, char **envp,
return -ENOMEM;

call_usermodehelper_setfns(info, init, cleanup, data);
+ info->wait_timeout = timeout;

return call_usermodehelper_exec(info, wait);
}
diff --git a/kernel/sys.c b/kernel/sys.c
index 9947fb0..a9079d1 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2013,7 +2013,7 @@ int orderly_poweroff(bool force)
goto out;
}

- ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_NO_WAIT,
+ ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_NO_WAIT, 0,
NULL, argv_cleanup, NULL);

out:
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index b8cc38c..28050ea 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -93,7 +93,7 @@ static void umh_keys_cleanup(struct subprocess_info *info)
static int call_usermodehelper_keys(char *path, char **argv, char **envp,
struct key *session_keyring, enum umh_wait wait)
{
- return call_usermodehelper_fns(path, argv, envp, wait,
+ return call_usermodehelper_fns(path, argv, envp, wait, 0,
umh_keys_init, umh_keys_cleanup,
key_get(session_keyring));
}
--
1.7.6.2


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